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Long-Term ENSO-Related Winter Rainfall Predictions over the Southeast U.S. Using the FSU Global Spectral Model
Title
Long-Term ENSO-Related Winter Rainfall Predictions over the Southeast U.S. Using the FSU Global Spectral Model.
Creator
Petraitis, Dawn C., O'Brien, James J., Clayson, Carol Anne, Jin, Fei-Fei, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description
Rainfall patterns over the Southeast U.S. have been found to be connected to the El Niño-Southern Oscillation (ENSO). Warm ENSO events cause positive precipitation anomalies and cold ENSO events cause negative precipitation anomalies. With this level of connection, models can be used to test the predictability of ENSO events. Using the Florida State University Global Spectral Model (FSUGSM), model data over a 50-year period will be evaluated for its similarity to observations. The FSUGSM is a...
Show moreRainfall patterns over the Southeast U.S. have been found to be connected to the El Niño-Southern Oscillation (ENSO). Warm ENSO events cause positive precipitation anomalies and cold ENSO events cause negative precipitation anomalies. With this level of connection, models can be used to test the predictability of ENSO events. Using the Florida State University Global Spectral Model (FSUGSM), model data over a 50-year period will be evaluated for its similarity to observations. The FSUGSM is a global spectral model with a T63 horizontal resolution (approximately 1.875°) and 17 unevenly spaced vertical levels. Details of this model can be found in Cocke and LaRow (2000). The experiment utilizes two runs using the Naval Research Laboratory (NRL) RAS convection scheme and two runs using the National Centers for Environmental Prediction (NCEP) SAS convection scheme to comprise the ensemble. The simulation was done for 50 years, from 1950 to 1999. Reynolds and Smith monthly mean sea surface temperatures (SSTs) from 1950-1999 provide the lower boundary condition. Atmospheric and land conditions from January 1, 1987 and January 1, 1995 were used as the initial starting conditions. The observational precipitation data being used as the basis for comparison is a gridded global dataset from Willmott and Matsuura (2005). Phase precipitation differences show higher precipitation amounts for El Niño than La Niña in all model runs. Temporal correlations between model runs and the observations show southern and eastern areas with the highest correlation values during an ENSO event. Skill scores validate the findings of the model/observation correlations, with southern and eastern areas showing scores close to zero. Temporal correlations between tropical Pacific SSTs and Southeast precipitation further confirm the model's ability to predict ENSO precipitation patterns over the Southeast U.S. The inconsistency in the SST/precipitation correlations between the models can be attributed to differences in the 200-mb jet stream and 500-mb height anomalies. Slight differences in position and strength for both variables affect the teleconnection between tropical Pacific SSTs and Southeast.
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Date Issued
2006
Identifier
FSU_migr_etd-1984
Format
Thesis
Wintertime ENSO Variability in Wind Direction Across the Southeast United States
Title
Wintertime ENSO Variability in Wind Direction Across the Southeast United States.
Creator
Culin, Joanne C., O'Brien, James J., Jin, Fei-Fei, Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description
Changes in wind direction in association with the phases of the El Niño-Southern Oscillation (ENSO) are identified over the Southeast region of the United States during the winter season (December-February). Wind roses, which depict the percentage of time the wind comes from each direction and can graphically identify the prevailing wind, are computed according to a 12-point compass for 24 stations in the region. Unfolding the wind rose into a 12-bin histogram visually demonstrates the peak...
Show moreChanges in wind direction in association with the phases of the El Niño-Southern Oscillation (ENSO) are identified over the Southeast region of the United States during the winter season (December-February). Wind roses, which depict the percentage of time the wind comes from each direction and can graphically identify the prevailing wind, are computed according to a 12-point compass for 24 stations in the region. Unfolding the wind rose into a 12-bin histogram visually demonstrates the peak frequencies in wind direction during each of the three (warm, cold and neutral) phases of ENSO. Normalized values represent the number of occurrences (counts) per month per ENSO phase, and comparison using percent changes illustrates the differences between phases. Based on similarities in wind direction characteristics, regional topography and results from a formal statistical test, stations are grouped into five geographic regions, with a representative station used to describe conditions in that region. Locations in South Florida show significant differences in the frequencies in wind direction from easterly directions during the cold phase and northerly directions during the warm phase. North Florida stations display cold phase southerly directions, and westerly and northerly directions during the warm phase, both of which are significant for much of the winter. Coastal Atlantic stations reveal winds from westerly directions for both phases. The Piedmont region demonstrates large variability in wind direction due to the influence from the Appalachian Mountains, but generally identifies warm phase and cold phase winds with more zonal influences rather than just from south or north. The Mountainous region also indicates southerly cold phase winds and northerly warm phase winds, but also reveals less of an influence from ENSO or significantly different distributions. Comparisons between observed patterns and those obtained using the NCEP/NCAR Reanalysis data reveal how the model-derived observations resolve the ENSO influence on surface wind direction at selected locations. Overall, resolution of the strength of the signals is not achieved, though the depiction of the general pattern is fair at two of the three locations. Connections between the synoptic flow and surface wind direction are examined via relationships to the storm track associated with the 250 hPa jet stream and sea level pressure patterns during each extreme ENSO phase. Discussion of reasons the NCEP reanalysis illustrates surface wind direction patterns different from those derived from observations is included.
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Date Issued
2006
Identifier
FSU_migr_etd-2946
Format
Thesis
Indexing, Mode Definition, and Signal Extraction in Climate Research
Title
Indexing, Mode Definition, and Signal Extraction in Climate Research: Analysis and Applications Involving the MJO, the AO, and ENSO.
Creator
Arguez, A. (Anthony), O’Brien, James J., Elsner, James B., Jin, Fei-Fei, Kim, Kwang-Yul, Liu, Guosheng, Nicholson, Sharon E., Department of Earth, Ocean and Atmospheric Sciences...
Show moreArguez, A. (Anthony), O’Brien, James J., Elsner, James B., Jin, Fei-Fei, Kim, Kwang-Yul, Liu, Guosheng, Nicholson, Sharon E., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description
There are two objectives of the present study. The primary objective is to undertake the following research projects involving the Arctic Oscillation (AO), the El Niño Southern Oscillation (ENSO), and the Madden Julian Oscillation (MJO): (1) an assessment of the utility of using Cyclo-stationary empirical orthogonal function (CSEOF) analysis to define the AO, (2) an empirical analysis of ENSO impacts based on varying indicator and impact regions, (3) detection and extraction of the MJO signal...
Show moreThere are two objectives of the present study. The primary objective is to undertake the following research projects involving the Arctic Oscillation (AO), the El Niño Southern Oscillation (ENSO), and the Madden Julian Oscillation (MJO): (1) an assessment of the utility of using Cyclo-stationary empirical orthogonal function (CSEOF) analysis to define the AO, (2) an empirical analysis of ENSO impacts based on varying indicator and impact regions, (3) detection and extraction of the MJO signal from QuikSCAT, and (4) the development of a general algorithm for determining optimal filter weights for time series endpoints. A secondary objective is to enumerate the statistical and analytical treatments of the AO, ENSO, and the MJO. This will include comparisons of how these three modes are defined (including their indices) and extracted from geophysical data sets. The AO is defined using empirical orthogonal function (EOF) analysis of sea level pressure north of 20'N. The resulting spatial pattern and time series captures the regional influence of its precursor, the North Atlantic Oscillation (NAO), which is a measure of mid-latitude zonal winds over the North Atlantic. ENSO was originally defined as the pressure difference between Tahiti and Darwin, Australia: the Southern Oscillation Index. Scientists now primarily use sea surface temperature (SST) anomalies averaged over one of the Ni'o regions as ENSO indices. The MJO was originally observed using spectral analysis of zonal wind time series in the Indian Ocean and Western Pacific. Present day researchers use extensions of EOF analysis to construct MJO time series. For all three climate modes, the creation of high quality space-time data sets has allowed for more sophisticated indices, supplanting the simpler point-based metrics. For the AO project, the cyclo-stationarity of Northern Hemisphere sea level pressure variability is considered. CSEOF analysis is an extension of EOF analysis that allows multiple spatial maps per mode. It accomplishes this by cyclically extending the covariance matrix based on a parameter called the nested period. By using a nested period of 12, a climate mode can be decomposed into a series of 12 monthly maps and an associated time series. Unlike EOF PC time series, which typically have larger amplitudes during winter months, CSEOF PC time series do not favor a particular season because the physical evolution of the climate mode is posited in the loading vectors (the maps) rather than the time series. This is impossible to accomplish with regular EOF analysis because it relegates each mode to one single map. A compelling case is made for a cyclo-stationary interpretation of AO variability. The leading CSEOF mode includes AO-type variability during a winter regime, as well as a summer regime characterized by pressure anomalies centered over Mongolia and associated with rainfall variability in the vicinity of the Ganges delta and eastern China. EOF modes that contribute to the resulting maps of the leading CSEOF mode are identified, including the eighth mode, which is deemed responsible for the summertime Asian pattern. CSEOF analysis of the AO mode only exemplifies the power of CSEOF analysis with regard to transferring a mode's physical evolution from a PC time series to a series of loading vectors. For the ENSO project, traditional ENSO impact analysis was recast to investigate the teleconnections between U.S. climate and varying indicator regions of SST anomalies in the tropical Pacific. This serves the dual purpose of finding a targeted indicator region for a particular impact zone (i.e. a localization of the teleconnection pattern) and indirectly assessing the viability of well-established ENSO indices (i.e. the Ni'o indices). Based on a selection of impact grid points with known ENSO responses, it appears that the most appropriate indicator region often varies from one impact grid point to another, as well as from warm SST phase to cold SST phase. In addition, air temperature composites behave differently than precipitation composites. In order to simultaneously consider the 'impact perspective' detailed above with the typical 'indicator perspective' (in which climate impacts are computed based on the well-established Ni'o indices), EOF analysis of composited climate fields, conditioned on SST phase, as functions of indicator region and impact zone was performed. The resulting modes represent indicator-impact pairs. Each mode has an impact amplitude function (a spatial temperature or precipitation anomaly signature over the impact region) and an associated indicator weighting function, which modulates the impact amplitude function based on the location of the indicator region. Based on this approach, the unusual yet well-established La Ni'a air temperature impact over the U.S. when using the Ni'o 1+2 region is accounted for as the superposition of two EOF modes. In addition, a teleconnection between tropical Pacific SST and Southeastern U.S. temperature anomalies is documented that is not related to ENSO. For the MJO project, wind data from the SeaWinds instrument on the QuikSCAT satellite are investigated to ascertain how well the surface manifestation of the MJO can be resolved. The MJO signal is detected in non-filtered gridded data using Extended EOF analysis of the zonal wind field, overshadowed by annual, semi-annual, and monsoon-related modes. After bandpass filtering with Lanczos weights, MJO signals are clearly detected in several kinematic quantities, including the zonal wind speed, the zonal pseudostress, and the velocity potential. Extraction of the MJO using QuikSCAT winds compares favorably with extraction using NCEP Reanalysis 2, except that the QuikSCAT signal appears to be more robust. For the filtering project, least squares techniques are utilized to retain endpoint intervals that are normally discarded due to filtering with convolutions in the time domain. The techniques minimize the errors between the pre-determined frequency response function (FRF) of interior points with FRF's that are to be determined for each position in the endpoint zone. The least squares techniques are differentiated by their constraints: (1) unconstrained, (2) equal-mean constraint, and (3) an equal-variance constraint. The equal-mean constraint forces the new weights to sum up to the same value as the pre-determined weights. The equal-variance constraint forces the new weights to be such that, after convolved with the input values, the expected variance is identical to the expected variance of the interior points. These 3 least squares methods are tested under three separate filtering scenarios and compared to each other as well as to the spectral filtering method, which is the standard of comparison. The results indicate that all 4 methods (including the spectral method) possess skill at determining suitable endpoints estimates. However, both the unconstrained and equal-mean schemes exhibit bias toward zero near the terminal ends due to problems with appropriating variance. The equal-variance and spectral techniques do not show evidence of this attribute and were never the worst performers. The equal-variance method showed great promise in the ENSO project involving a 5-month running mean filter, and performed at least on par with the other methods for virtually all time series positions in all three filtering scenarios.
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Date Issued
2005
Identifier
FSU_migr_etd-7032
Format
Thesis
Interannual Flows along Australia's Western and Southern Coasts and along the Northern Coast of the Gulf of Mexico
Title
Interannual Flows along Australia's Western and Southern Coasts and along the Northern Coast of the Gulf of Mexico.
Creator
Li, Jianke, Clarke, Allan J., Jin, Fei-Fei, Dewar, William, Nof, Doron, Iverson, Richard, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description
The purpose of this dissertation is to study the interannual flows along the western and southern Australian coasts and along the northern coast of the Gulf of Mexico. Along the western and southern Australian coasts, sea levels are highly correlated with the El Ni˜no signal due to the leak in the gappy western equatorial Pacific Ocean boundary. Along the western Australian coast the coastline is nearly meridional and particle displacements near the coast undergo a change in Coriolis...
Show moreThe purpose of this dissertation is to study the interannual flows along the western and southern Australian coasts and along the northern coast of the Gulf of Mexico. Along the western and southern Australian coasts, sea levels are highly correlated with the El Ni˜no signal due to the leak in the gappy western equatorial Pacific Ocean boundary. Along the western Australian coast the coastline is nearly meridional and particle displacements near the coast undergo a change in Coriolis parameter. In order to keep the potential vorticity constant, this interannual coastal signal should propagate westward as Rossby waves with large zonal scale. TOPEX/Poseidon sea level data and coastal tide gauge measurements do show these large-scale waves off Australia's northwest coast. Along Australia's nearly zonal southern coast, particle displacements are nearly zonal near the coast and experience no planetary vorticity change. Consequently the Rossby wave mechanism fails and theory suggests that the signal should decay from the shelf edge with baroclinic Rossby radius of deformation scale. High-resolution along-track TOPEX/Poseidon sea level heights show that the interannual height signal does decay rapidly seaward of the shelf edge with this scale. The sharp fall in sea level and geostrophic balance imply strong (10 cm/sec) low frequency currents seaward of the shelf edge. On the shelf, inter annual flow is in the same direction as the shelf edge flow but much weaker. The anomalous flows tend to be eastward during La Ni˜na, when the western equatorial Pacific and Australian coastal sea levels are unusually high, and westward during El Ni˜no when coastal sea levels tend to be anomalously low. The anomalous low-frequency flows can transport larvae large distances, enhancing the recruitment of Australian salmon to nursery grounds in the eastern part of the southern coast when the coastal sea level is higher than normal and decreasing recruitment when it is lower than normal. Along the shelf edge south of 23oS of the western Australian coast, although the coastline is nearly meridional, high resolution satellite sea level estimates show that the inter annual sea level signal does not have the expected large spatial scale as it decreases rapidly seaward from the shelf edge. The drop in interannual sea level amplitude coincides with the mean position of the Leeuwin Current. Theory shows that a nearly meridional mean flow, as in the case of the Leeuwin Current, can induce this fall in interannual signal amplitude by altering the potential vorticity balance. The associated interannual shelf-edge flow tends to strengthen the Leeuwin Current during La Ni˜na, weaken it during El Ni˜no and may profoundly affect the recruitment of the western rock lobster. Past work has shown that the interannual wind stress curl in the North Atlantic generates Rossby waves that reach the eastern U.S. coast and affect coastal sea levels both there and along the northern coast of the Gulf of Mexico. Tide gauge and TOPEX/Poseidon satellite sea level height measurements show that this signal penetrates all the way around the Gulf shelf to the Yucatan Peninsula, local alongshore interannual wind stress increasing the signal amplitude between Pensacola and the Texas-Louisiana shelf. In accordance with theory, satellite observations show that the seaward spatial structure of the sea levels and the associated geostrophic flows depend on the angle of the coastline with respect to due north and the Loop Current mean shelf edge flow. Off the eastern boundary (small) formed by the west coast of Florida, the Loop Current distorts the potential vorticity balance and the sea level falls rapidly from the shelf edge with a scale of order the Loop Current width. Off the northern boundary ( 90o), the signal behaves as a coastal Kelvin wave, the sea level amplitude falling quickly away from the shelf edge with first baroclinic radius of deformation scale. Off the western boundary ( 180o), the interannual sea level amplitude falls rapidly seaward of the shelf edge consistent with short western boundary scales. Geostrophic shelf edge flow may reach amplitudes of order 10cms−1 but along shelf flow amplitudes are a few cm/s or less. Even so, weak shelf flows of low frequency can transport particles many hundreds of kilometers.
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Date Issued
2004
Identifier
FSU_migr_etd-3076
Format
Thesis
Coexistence of Leading Equatorial Coupled Modes for ENSO
Title
Coexistence of Leading Equatorial Coupled Modes for ENSO.
Creator
Bejarano-Avendano, Luis Fernando, Jin, Fei-Fei, Liu, Guosheng, Zou, Xiaolei, Cai, Ming, Clarke, Allan, O'Brien, James J., Program in Geophysical Fluid Dynamics, Florida State...
Show moreBejarano-Avendano, Luis Fernando, Jin, Fei-Fei, Liu, Guosheng, Zou, Xiaolei, Cai, Ming, Clarke, Allan, O'Brien, James J., Program in Geophysical Fluid Dynamics, Florida State University
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Abstract/Description
A comprehensive eigen-mode analysis of an intermediate coupled model linearized with respect to arrays of basic states is performed to study the regimes of leading ocean-atmosphere coupled modes of relevance to the El Niño Southern Oscillation phenomenon. Different kinds of leading modes are found to coexist and to become unstable under wide ranges of basic states and parameter conditions. In particular, two main kinds of modes have periods around 4 years and 2 years. They are thus referred...
Show moreA comprehensive eigen-mode analysis of an intermediate coupled model linearized with respect to arrays of basic states is performed to study the regimes of leading ocean-atmosphere coupled modes of relevance to the El Niño Southern Oscillation phenomenon. Different kinds of leading modes are found to coexist and to become unstable under wide ranges of basic states and parameter conditions. In particular, two main kinds of modes have periods around 4 years and 2 years. They are thus referred as to quasi-quadrennial (QQ), quasi-biennial (QB) modes, respectively. The positive coupled feedback destabilizes and quantizes the near-continuous spectrum for the low-frequency modes of the upper ocean dynamics giving rise to these leading modes with distinct periodicities. The QQ mode can be understood to a large extent by the mechanisms elucidated in the simple conceptual recharge oscillator which relays on slow oceanic dynamic adjustment of equatorial heat content, whereas anomalous advection of sea surface temperature by equatorial zonal current anomalies plays an important role in the QB mode. One of the findings of this study is that the QQ and QB mode may coalesce under realistic conditions through a codimension-2 degeneracy in the parameter space. The coexistence or multiplicity of ENSO-related coupled modes under present climate conditions may provide a plausible explanation for the observed dominating QQ and QB variability of rich ENSO behaviors.
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Date Issued
2006
Identifier
FSU_migr_etd-1210
Format
Thesis